this is a normal thing, as you have said, and is particularly common in runners. if there are no other symptoms, i would not think anything of it. the more tests an allopath gives, the more likely they will come up with something that is "wrong" and a pill or disfigurement to "correct" it. i believe normal healthy menses to be a spot or two at most.
herbs are just food. the body will take what it needs and eliminate the rest, same as with anything else that is human food.